Bubble Collapse and Liquid Jet Formation in Non-Newtonian Liquids

摘要

The production of shock waves and liquid jets by cavitation bubbles is a major cause of wear in many fluid mechanical devices that generate high-speed flows, and hence negative pressures in liquids(Treen, 1987). A study of the effects of polymer additives on lubricant flow in journal bearings indicate that their role in reducing wear may be associated with the mitigating effects of viscoelasticity on cavitation (Berker et al., 1995), but the precise nature of such effects remains unclear. Fluid elasticity might be expected to play a mitigating role in cavitation damage, given sit ability to reduce the nonsphericity of cavities in shear fields (Young, 1989): this reduces the tendency for jet formation, as it is the asymmetry of collapse (as a result of a pressure gradient across the cavity) that results in jet formation. Where the pressure gradient arises from the presence of a solid boundary, the resultant jet is directed onto the surface. Jet formation also arises due to cavity collapse under the cation of transient pressure pulses, such as shock waves, and this mechanism may lead to the development of liquids jets of enhanced potency, in terms of their ability to damage surfaces. The experiments reported here exploit a new technique that was developed to facilitate studies of the influence of fluid elasticity on this mechanism.